5 449
1850 (the deaf and dumb) 9,803 423
1860 (the deaf and dumb) 12,821 408
1870 (the deaf and dumb) 16,205 420
1880 (deafness occurring under sixteen) 33,878 675
1890 (the deaf and dumb) 40,592 648
1900 (the totally deaf) 37,426 492
1910 (the deaf and dumb) 43,812 476

From this table there appears to be a steady decrease in the number of
the deaf in relation to the general population from 1830 to 1860, this
latter year seeming to be the low water mark. From 1860 to 1870 there is
a slight increase, and from 1870 to 1880 a very large one, due to some
extent to the method of taking the census. From 1880 to 1890 there is a
certain decrease, though the proportion is still very high. From 1890 to
1900 there is a very considerable decrease, probably indicating a return
to true conditions; and a not negligible decrease from 1900 to 1910.

On the whole, with respect to these statistics, probably the most that
we can safely say is that deafness is at least not on the increase
relatively among the population, while there is a possibility that at
present it is decreasing. For further determinations, we shall have to
seek other means of inquiry.

THE ADVENTITIOUSLY DEAF AND THE CONGENITALLY DEAF

We may perhaps best approach the problem of deafness as an increasing or
decreasing phenomenon in the population, if we think of the deaf as
composed of two great classes: those adventitiously deaf, that is, those
who have lost their hearing by some disease or accident occurring after
birth, and those congenitally deaf, that is, those who have never had
hearing.[17] In regard to the former class, it follows that we are
largely interested in the consideration of those diseases, especially
those of childhood, which may affect the hearing, and in their
prevention or diminution we can endeavor to ascertain how far there are
possibilities of reducing the number of the deaf of this class. In the
latter case we are called upon to examine some of the great problems
involved in the study of heredity, especially in respect to the extent
that the offspring is affected by defects or abnormalities of the
parent, and to see what, if any, means are at hand to alter conditions
that bring about this form of deafness. We shall first discuss the
causes of adventitious deafness, together with th